Abstract
In-tube condensation of refrigerants is an important process which affects thermal efficiency in many applications, ranging from refrigeration and air conditioning to electronics thermal management. In-tube heat transfer and pressure drop are important to heat exchanger sizing and design. In this work, micro- and nanostructured surfaces are applied to the internal wetted areas of copper and aluminum mini-channels to enhance the condensation heat transfer coefficient of hydrofluorocarbon R1233zd(E) refrigerant. To achieve scalable nanomanufacturing, surfaces were uniformly structured by relying on hydrochloric acid etching of aluminum and chemical oxidation of copper. The etched aluminum surfaces exhibited a 150% increase in heat transfer coefficient compared to smooth aluminum channels at specific qualities, with a 66% heat transfer coefficient improvement for complete phase change from saturated vapor to saturated liquid. Copper oxide structures showed no discernable difference in thermal-hydraulic performance when compared to smooth copper channels. Critical dimensionless parameters governing the heat transfer enhancement were identified by varying the tube internal diameter (2.3 mm to 4.7 mm), refrigerant mass flux (50 to 300 kg/(m2·s)), and refrigerant quality (0 to 1). The dimensionless parameters include the Bond number normalized to the condensate film thickness, and the Weber number modified by the vapor friction factor. The relatively small increase in pressure drop (< 10%) associated with these surface enhancements further supports the promise of this method. The scalable and cost-effective techniques used to create these aluminum microstructures may reduce manufacturing cost when compared with current enhancement approaches such as extrusion, drawing, and welding.
Original language | English |
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Article number | 124012 |
Journal | International Journal of Heat and Mass Transfer |
Volume | 207 |
DOIs | |
State | Published - Jun 15 2023 |
Funding
The authors gratefully acknowledge funding support from the Air Conditioning and Refrigeration Center (ACRC), the Office of Naval Research (ONR) under Grant No. N00014-21-1-2089, the National Science Foundation under Award No. 1554249, and the Center for Integrated Thermal Management of Aerospace Systems (CITMAV). N.M. gratefully acknowledges funding support from the International Institute for Carbon Neutral Energy Research (WPI-I2CNER), sponsored by the Japanese Ministry of Education, Culture, Sports, Science and Technology. XPS, SEM, AFM and FIB were carried out in part in the Materials Research Laboratory Central Facilities, University of Illinois. The authors gratefully acknowledge funding support from the Air Conditioning and Refrigeration Center (ACRC), the Office of Naval Research ( ONR ) under Grant No. N00014-21-1-2089 , the National Science Foundation under Award No. 1554249 , and the Center for Integrated Thermal Management of Aerospace Systems ( CITMAV ). N.M. gratefully acknowledges funding support from the International Institute for Carbon Neutral Energy Research ( WPI-I2CNER ), sponsored by the Japanese Ministry of Education, Culture, Sports, Science and Technology . XPS, SEM, AFM and FIB were carried out in part in the Materials Research Laboratory Central Facilities, University of Illinois.